Forward Osmosis / CEDI Desalination

Nrgtek has developed a novel process for seawater desalination using forward osmosis coupled with “continuous electro-deionization” for treatment of saline water. The team has successfully completed a DOE- SBIR Phase I & II project on “solar-assisted forward osmosis membranes and seawater desalination". New draw solutions with osmotic pressures in excess of 225 atms and cloud points below 40C have been synthsized, as well as high ionic conductivity membranes for the CEDI module (1 S/cm), with high ionic transfer capacity.

Unlike reverse osmosis (RO) processes, which employ high pressures ranging from 400-1100 psi to drive fresh water through a salt-rejection membrane, FO/CEDI technology uses the natural osmotic pressures of solutions to effect fresh water separation. A ‘draw solution’, having a significantly higher osmotic pressure than the saline feed-water, flows along the permeate side of the membrane, and water naturally transports itself across the membrane by osmosis.

Osmotic driving forces in FO can be significantly greater than hydraulic driving forces in RO, leading to higher water recovery. Thus, Nrgtek’s FO system is non-pressurized, allowing design with lighter, compact, and less expensive materials. These factors translate into savings in both capital and operational costs. The CEDI system takes the diluted draw solution stream from the FO permeate and reconcentrates it back to high concentration, high osmotic pressure solutions for recycling to the FO step. This is made possible by special ion exchange membranes with very high conductivity and transfer capapcities.